PLENTIFUL ENERGY

CHAPTER 8
THE PYROPROCESS
In the next three chapters we wish to provide an understanding of the
electrochemical portion of the IFR spent fuel process, electrorefining—the heart of
IFR pyroprocessing—what it can do, and importantly, what it can't do. In this
chapter we will describe the processes, equipment, results, and status of IFR
pyroprocessing. The following chapter will deal with the chemistry itself, and the
final one will cover the application to LWR spent fuel. It shares some but not all the
characteristics of electro refining. After that, the waste processes will be discussed
in some detail.
It is fair to ask why we need any process at all. The answer is straightforward. In
any reactor, for any fuel, there is a strict limit to the fuel “burnup” beyond which
the fuel cladding will “fail.” It may just be a pinhole which leaks radioactive fuel
material into the coolant, or it may be worse; it may breach wide open, leaking
quantities of radioactivity into the coolant. This contaminates the entire primary
system, which is serious in that it makes personnel access difficult if the reactor
design is such that routine access is required, or it may be of limited importance if
such access is not normally required. Our cladding is steel. It is damaged gradually
by exposure to neutrons, particularly those at the highest energies, and eventually it
becomes brittle and subject to puncture or breach, either by contact with the fuel it
contains, or by internal pressure from the buildup of fission gases. The fuel must
come out of the reactor in a safe amount of time, well before these things can
happen. In the IFR, as it is for most reactors, that time is three or four years. When
it comes out it must be “reprocessed” so it can be “re-fabricated” into fresh fuel
and returned to the reactor for another cycle.
The fuel must also be recycled for both economic and resource reasons. The
higher fissile content of the IFR spent fuel, which has a fissile percentage about
twenty times that of LWR, makes its recycle and reuse mandatory for good
economics. And it is recycle, recharging the same fuel over and over again, that
allows the huge extension of fuel resources of the IFR. Further, a substantial
fraction of the new plutonium is bred in the depleted uranium blankets surrounding
the core and processing is needed to recover it. And finally, processing allows
removal of the very long-lived isotopes from the nuclear waste.
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